by Zarquon, published
This is a rough 1/8 scale model of my teams entry into Punkin Chunkin ( http://www.punkinchunkin.com/ ). There is a good deal of tuning which goes into a trebuchet and it's difficult to work it all out full scale since we only get some many shots between repairs. This model is to facilitate tuning work. Also just for fun. We enter purely for fun and our budget it way on the low side to be competitive but that's no excuse not to tune up.
At full scale the treb is 12 feet tall to the pivot and uses 1000lbs (1400 with add-ons) counterweight to throw 8 lbs pumpkins. Simulations show a maximum range of a bit over 800 feet. Our best throws are only a bit over 400.
At 1/8 scale it's about 18 in tall to the pivot, uses 2lbs counterweight and throws .25 ounce marbles. The first few days of throwing show a range of about 55 feet. The simulated max range is about 100 feet so there is tuning to do.
Give enough time I would like to add a more efficient whipper style arm to the model/machine.
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Print 2 of each part except the pivot.
Cut the following lengths of 5/16 (8mm) rod: 6x20in 4x18in 2x9in 3x4in
1x34.5in (hardwood for this one if available)
Other things you will need: 2x 608 bearings 1x5-6in 5/16 threaded rod 2-4 nuts for the threaded rod eye screw with threads ground out for firing pin finishing nail for sling release String for rigging pouch for sling tent stakes to hold it down 2lbs of weight .25 ounce projectiles (large marbles)
Some rods fit in tightly for me and others I had to glue. In any case you will want to at least glue the diagonal supports into the base corners and the bearings into the holders as those will pull out as the weight swings. The pivot will slide on the hardwood rod and should also be secured. The pivot should be located 24in from one end of the arm. The sling length should be 21 in.